1. Field of the Invention
The present invention relates to a thermosensitive recording material, and more particularly to a thermosensitive recording material having a substrate and a thermosensitive coloring layer which is formed on the substrate and which can induce color formation upon application of heat.
2. Discussion of the Related Art
A thermosensitive recording material having a substrate such as paper or a film and a thermosensitive coloring layer which is formed on the substrate and which includes a color forming composition is well known. Colored images can be formed on the recording material upon application of heat with a thermal printhead, a heat pen or the like. The thermosensitive recording material is used as recording sheets for various recording apparatus. The thermosensitive recording material generally has a drawback in that recorded images are erased, or non-image areas are colored when the recording material contacts water, oils or various chemicals. In attempting to solve this problem, it is proposed to form a protective layer on the thermosensitive coloring layer.
For example, Japanese Laid-Open Patent Publications Nos. 54-128347, 54-3594, 56-126193 and 56-13993 have disclosed thermosensitive recording materials including a protective layer including a water-soluble resin. In addition, Japanese Laid-Open Patent Publications Nos. 57-188392, 64-61287 and 60-68990 have disclosed thermosensitive recording materials including a protective layer including a water-soluble resin together with a water-resistant applying agent. However, these recording materials cannot entirely improve the resistance to chemicals and have a drawback of poor ability to be used with thermal printheads. Further, Japanese Laid-Open Patent Publications Nos. 5-69665, 6-239019 and 5-318926 have disclosed thermosensitive recording materials including a protective layer which is formed by coating with a liquid including a core-shell type resin emulsion (the core-shell type resin emulsion means a resin emulsion in which particles of the resin which have two or more layers are emulsified). However, these recording materials cannot entirely improve the resistance to chemicals and the ability to be used with thermal printheads, and further have a drawback in that the protective layers thereof have much worse resistance to cracking than the protective layers including a water-soluble resin mentioned above.
Because of these reasons, a need exists for a thermosensitive recording material having good resistance to water and chemicals, good ability to be used with thermal printheads and good color forming properties without occurrence of cracking of the protective layer.